Publication number | US6369813 B2 |

Publication type | Grant |

Application number | US 09/109,257 |

Publication date | Apr 9, 2002 |

Filing date | Jun 30, 1998 |

Priority date | Jun 30, 1998 |

Fee status | Paid |

Also published as | US20020008698 |

Publication number | 09109257, 109257, US 6369813 B2, US 6369813B2, US-B2-6369813, US6369813 B2, US6369813B2 |

Inventors | Vladimir Pentkovski, Deep Buch, Michael K. Dwyer, Hsien-Hsin Lee, Hsien-Cheng E. Hsieh |

Original Assignee | Intel Corporation |

Export Citation | BiBTeX, EndNote, RefMan |

Patent Citations (7), Referenced by (9), Classifications (6), Legal Events (4) | |

External Links: USPTO, USPTO Assignment, Espacenet | |

US 6369813 B2

Abstract

The present invention is directed to a method and apparatus for processing normalized meshes. The normalized meshes are formed by N polygons which have M vertices. M vertex coordinates are stored in a vertex array corresponding to the M vertices of the N polygons. N polygon indices are stored in an index array. Each of the N polygon indices references a predetermined number of the M vertex coordinates. A first subset of the index array having N**1 **polygon indices is determined. A second subset of the vertex array is selected such that the second subset contains M**1 **vertex coordinates corresponding entirely to the N**1 **polygon indices in the first subset. The second subset defines a window having a small size relative to the vertex array. The M**1 **vertex coordinates in the second subset are processed to generate processed data. The processed data are then concurrently sent to a graphics processor in an on-line manner.

Claims(20)

1. A method comprising:

storing M vertex coordinates in a vertex array corresponding to M vertices of N polygons, and N polygon indices in an index array, each of the N polygon indices referencing a predetermined number of the M vertex coordinates;

normalizing the vertex array such that a first subset of the vertex array containing M**1** vertex coordinates are referenced by a second subset of the index array containing N**1** polygon indices, the second subset defining a window having a small size relative to the vertex array; and

processing the M**1** vertex coordinates in the first subset to generate processed data for further processing or displaying.

2. The method of claim 1 further comprising:

updating the window by selecting a third subset of the vertex array such that the third subset contains M**2** vertex coordinates corresponding entirely to N**2** polygon indices in a fourth subset of the index array while sliding the window along the vertex array until the entire vertex array has been processed.

3. The method of claim 1 further comprising concurrently sending the processed data to a graphics processor in an on-line manner.

4. The method of claim 1 wherein normalizing comprises:

determining a window of reference in the vertex array having a small size relative to the vertex array;

determining a vertex reference from one of polygon indices in the index array; and

if the vertex reference lies outside the window of reference,

copying the vertex reference to a neighborhood of the window of reference, and

updating the window of reference to include the copied vertex reference.

5. The method of claim 4 further comprising:

updating the vertex array; and

updating the index array.

6. The method of claim 5 wherein updating the vertex array includes re-arranging the vertex coordinates in the vertex array to include the updated window of reference.

7. The method of claim 5 wherein updating the index array includes replacing the vertex reference by a new reference to the copied vertex reference.

8. The method of claim 6 wherein updating the index array includes changing the vertex references to point to the updated vertex array.

9. An apparatus comprising:

an index array to store polygon indices corresponding to meshes;

a vertex buffer coupled to the index array to store vertex information in a normalized vertex array, the normalized vertex array having a first subset containing M**1** vertex coordinates referenced by a second subset of the index array; and

an address generator coupled to the index array and the vertex array to address the vertex buffer based on the second subset of the index array.

10. The apparatus of claim 9 further comprising:

a graphics engine coupled to the vertex buffer to receive the vertex information, the graphics engine performing a graphic transformation to the vertex information.

11. The apparatus of claim 9 further comprising:

a data fetcher coupled to the vertex buffer to fetch vertex information from a memory via a graphic bus upon receiving a control signal; and

a multiplexer coupled to the vertex buffer, the data fetcher, and the graphics engine to select vertex information to the graphics engine.

12. A system comprising:

a bus; and

a processor coupled to the bus, the processor comprising:

an index array to store polygon indices corresponding to the polygon meshes,

a vertex buffer coupled to the index array to store vertex information in a normalized vertex array, the normalized vertex array having a first subset containing M**1** vertex coordinates referenced by a second subset of the index array, and

an address generator coupled to the index array and the vertex array to address the vertex buffer based on the second subset of the index array.

13. The system of claim 12 further comprising:

a graphics engine coupled to the vertex buffer to receive the vertex information, the graphics engine performing a graphic transformation to the vertex information.

14. The system of claim 12 further comprising:

a data fetcher coupled to the vertex buffer to fetch vertex information from a memory via a graphic bus upon receiving a control signal; and

a multiplexer coupled to the vertex buffer, the data fetcher, and the graphics engine to provide vertex information to the graphics engine.

15. A system comprising:

a bus;

a memory coupled to the bus, the memory storing instructions; and

a processor coupled to the bus and the memory, the processor executing the instructions to at least:

store M vertex coordinates in a vertex array corresponding to the M vertices of the N polygons, and N polygon indices in an index array, each of the N polygon indices referencing a predetermined number of the M vertex coordinates,

normalize the vertex array such that a first subset of the vertex array containing M**1** vertex coordinates are referenced by a second subset of the index array containing N**1** polygon indices, the second subset defining a window having a small size relative to the vertex array, and

process the M**1** vertex coordinates in the first subset to generate processed data for further processing or displaying.

16. The system of claim 15 wherein the processor further executes the instructions to:

update the vertex array by re-arranging the vertex coordinates in the vertex array to include the updated window of reference; and

update the index array by changing the vertex references to point to the updated vertex array.

17. The system of claim 15 wherein the processor further executes the instructions to:

update the index array by replacing the vertex reference by a new reference to the copied vertex reference.

18. The system of claim 15 wherein the processor executing instructions to normalize the vertex array executes instructions to:

determine a window of reference in the vertex array;

determine a vertex reference from one of the polygon indices in the index array; and

if the vertex reference lies outside the window of reference,

copy the vertex reference to a neighborhood of the window of reference, the vertex reference occupying at least two entries in the vertex array, and

update the window of reference to include the copied vertex reference.

19. The system of claim 18 wherein the processor further executes the instructions to transform the M**1** vertex coordinates according to a graphic transformation.

20. The system of claim 18 wherein the small size is less than or equal to a predetermined size.

Description

1. Field of the Invention

This invention relates to graphic processing. In particular, the invention relates to graphic processing using polygon meshes.

2. Description of Related Art

In three-dimensional (3-D) graphics, objects are represented using a number of techniques such as polygon mesh, modeling, etc. Among these techniques, polygon mesh representation is popular.

In polygon mesh representation, an object is represented by a mesh of polygonal facets. In the general case, an object has curved surfaces and the facets are an approximation to such a surface. A polygon mesh representation is a geometric and topological description of the boundary or surface of the object. A polygon mesh is a structure that consists of polygons represented by a list of (x, y, z) coordinates that are the polygon vertices. Thus the information stored to describe the object is a list of coordinates of points or vertices.

When a 3-D object is processed by a processor in a computer system, the processing time depends on a number of factors. One of the important factors is the memory referencing time to retrieve the information describing the objects such as the list of vertex coordinates. In 3-D graphics processing, the list of vertex coordinates are usually indexed or referenced by the corresponding polygon indices. The processing of the polygons involving the indexing of the vertex coordinates and transformation calculations is referred to as the geometry computations.

On-line driver is a method that allows the commands to a graphics controller (GC) to be sent to the GC concurrently with the geometry computations to speed up the overall processing time. However, when the size of the indexed primitives is large, such as in complex 3-D scenes, the on-line driver becomes inefficient. The reason for this inefficiency is that if the GC does not support indexed primitives, as is often the case, the entire pool of indexed primitives has to be stored in an intermediate buffer and the vertex information is sent to the GC on a polygon-by-polygon basis. This will eliminate the gain of concurrent processing and cause dirty writebacks from the intermediate buffer which incurs additional overhead.

Therefore there is a need in the technology to provide an efficient method and apparatus to process the polygon meshes for 3-D graphics.

The present invention is directed to a method and apparatus for processing normalized meshes. The normalized meshes are formed by N polygons which have M vertices. The M vertex coordinates are stored in a vertex array corresponding to the M vertices of the N polygons. N polygon indices are stored in an index array. Each of the N polygon indices references a predetermined number of the M vertex coordinates. A first subset of the index array having N**1** polygon indices is determined. A second subset of the vertex array is selected such that the second subset contains M**1** vertex coordinates corresponding entirely to the N**1** polygon indices in the first subset. The second subset defines a window having a small size relative to the vertex array. The M**1** vertex coordinates in the second subset are processed to generate processed data. The processed data are then concurrently sent to a graphics processor in an on-line manner.

The features and advantages of the present invention will become apparent from the following detailed description of the present invention in which:

FIG. 1 is a diagram illustrating one embodiment of a computer system **100** in which one embodiment of the present invention may be utilized.

FIG. 2 is a diagram illustrating a three-dimensional (3-D) object represented by polygons according to one embodiment of the invention.

FIG. 3 is a diagram illustrating arrays for processing unnormalized meshes according to one embodiment of the invention.

FIG. 4 is a diagram illustrating arrays for processing normalized meshes according to one embodiment of the invention.

FIG. 5 is a diagram illustrating arrays for processing normalized meshes using windows according to one embodiment of the invention.

FIG. 6 is a diagram illustrating a performance curve according to one embodiment of the invention.

FIG. 7 is a flow diagram illustrating a process to process normalized meshes according to one embodiment of the invention.

FIG. 8 is a diagram illustrating a mesh processor according to one embodiment of the invention.

FIG. 9 is a flow diagram illustrating a process to normalize meshes with same window size according to one embodiment of the invention.

FIG. 10 is a flow diagram illustrating a process to normalize meshes with different window sizes according to one embodiment of the invention.

FIG. 11 is a diagram illustrating an example of a set of triangles according to one embodiment of the invention.

FIG. 12 is a diagram illustrating arrays for processing unnormalized meshes in the example of FIG. 11 according to one embodiment of the invention.

FIG. 13A is a diagram illustrating spikes in a performance curve caused by processing unnormalized meshes in the example of FIG. 11 according to one embodiment of the invention.

FIG. 13B is a diagram illustrating the reference pointers stored in the triangle index array for the unnormalized meshes in the example of FIG. 11 according to one embodiment of the invention.

FIG. 14 is a diagram illustrating arrays for processing normalized meshes in the example of FIG. 11 according to one embodiment of the invention.

FIG. 15A is a diagram illustrating a performance curve for processing normalized meshes with separated vertex windows in the example of FIG. 11 according to one embodiment of the invention.

FIG. 15B is a diagram illustrating the reference pointers stored in the triangle index array for the normalized meshes in the example of FIG. 11 according to one embodiment of the invention.

The present invention is directed to a method and apparatus for processing normalized meshes in three-dimensional (3-D) graphics. Normalized meshes allow efficient use of cache memory by confining references to within windows of memory. Mesh normalization is performed by iteratively searching for an optimal window size for the vertex array while copying referenced vertex information to the local window. During real-time processing of the 3-D objects represented by normalized meshes, the geometry engine uses the predetermined window to reference the vertices. After processing, the geometry engine writes the transformed vertices to the graphics controller in an on-line fashion. This method of processing eliminates dirty writebacks by keeping the window small, and the on-line driver allows concurrency of processing and writing, thereby improving the overall graphic processing throughput.

In the following description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice the present invention. In other instances, well known electrical structures and circuits are shown in block diagram form in order not to obscure the present invention.

FIG. 1 is a diagram illustrating one embodiment of a computer system **100** in which one embodiment of the present invention may be utilized. Computer system **100** comprises a processor **110**, a host bus **115**, a PCI bridge **120**, a storage device **135**, an advanced graphics processor **125**, a mesh processor **132**, a video monitor **127**, a PCI bus **140**,

The host processor **110** represents a central processing unit of any type of architecture, such as complex instruction set computers (CISC), reduced instruction set computers (RISC), very long instruction word (VLIW), or hybrid architecture. The processor **110** is coupled to the PCI bridge **120** via a host bus **115**. While this embodiment is described in relation to a single processor computer system, the invention could be implemented in a multi-processor computer system.

The PCI bridge **120** provides an interface between the host bus **115** and a PCI bus **140**. The PCI bridge **120** also provides the graphic port, e.g., Accelerated Graphics Port (AGP), or the graphics bus **122** for connecting to a graphics controller or advanced graphics processor **125**. The graphics controller **125** is interfaced to a video monitor **127**. The video monitor **127** displays graphics and images rendered or processed by the graphics controller **125**. The PCI bridge **120** also provides an interface to the storage device **135**.

The storage device **135** represents one or more mechanisms for storing data. For example, the storage device **135** may include read only memory (ROM), random access memory (RAM), magnetic disk storage mediums, optical storage mediums, flash memory devices, and/or other machine-readable mediums. FIG. 1 also illustrates that the storage device **135** has stored therein data **137** and program code **136**. The data **137** stores graphics data and temporary data. Program code **136** represents the necessary code for performing any and/or all of the techniques in the present invention. Of course, the storage device **135** preferably contains additional software (not shown), which is not necessary to understanding the invention.

The PCI bus **140** represents an expansion bus that allows the processor **110** to communicate with a number of peripheral devices. The PCI bus **140** provides an interface to a PCI-to-ISA/EISA bridge **145**, PCI devices **150** _{1 }to PCI device **150** _{N}. The PCI devices **150** _{1 }to **150** _{N }represent any device that is interfaced to the PCI bus **140**. Examples of PCI devices are fax/modem controller, audio card, network controller, etc.

The PCI-to-ISA/EISA bridge **145** represents an interface device between the PCI bus **140** and an ISA/ EISA bus **160**. The ISA/ EISA bus **160** represents a peripheral bus that interfaces to a number of peripheral devices, including an ISA device **162**, an EISA device **164**. Example of an ISA/ EISA device includes a parallel input/output (I/O) device, a serial communication interface device.

FIG. 2 is a diagram illustrating a three-dimensional (3-D) object **200** represented by polygons according to one embodiment of the invention. The object **200** is represented by a number of triangles **210** _{i }where i=1, . . . , N (N is a positive whole number) and the representation information is stored in a mesh pool **220**. As is known by one skilled in the art, other types of polygon other than the triangle can be employed.

Each of the triangles **210** _{i }is represented by three vertices. For example, triangle **210** _{k }is represented by three vertices A, B, and C. The three vertices A, B, and C form a surface which will be rendered by the processor or graphics controller. The surface formed by the three vertices A, B, and C are determined by the coordinates of the vertices A, B, and C. The complete object **200** is described by the list of the triangles **210** _{i }(i=1, . . . , N) and the list of the corresponding vertex coordinates which are stored in the mesh pool **220**.

The mesh pool **220** stores the representation information of the object **200**. The mesh pool includes a vertex array V **230** and a triangle index array T **240**. In one embodiment, a portion of the vertex array V **230** and the triangle index array T **240** is located in a cache memory which can be referenced locally by a processor.

The vertex array V **230** stores the coordinates of the vertices of the triangles **210** _{i }(i=1, . . . , N). For 3-D objects, these coordinates are the (x, y, z) components in a 3-D coordinate system. The number of entries in the vertex array V **230** depends on the number of triangles **210** _{i }(i=1, . . . , N), or the number N, and the manner these triangles are interconnected in the meshes. A vertex in one triangle may be also be a vertex of one or more triangles in the meshes. Because of this redundancy, the number of entries in the vertex array V **230** usually exceeds N. For a complex 3-D object which has a large number of triangles, the number of entries in the vertex array V **230** may be quite large. For example, assuming the number of triangles for a 3-D object is 100,000 and the redundancy is 3 (i.e., each vertex belongs to three triangles on the average), then the total number of entries is 300,000. Each entry has 3 coordinate values. Assume further that each coordinate value is represented by a 32-bit floating point number, then each entry requires 12 bytes. The vertex array V **230** therefore would need a storage amount of approximately 3.6 MB. This amount of storage exceeds the normal size of typical cache memory. The vertex array V **230** is therefore usually stored in main memory and blocks of data are transferred to the cache memory when needed. If the references of these vertices by the triangle index array T **240** are not within the cache locality, dirty writebacks are needed. These writebacks will incur additional processing time.

The triangle index array T **240** stores the triangle indices and the corresponding vertex references. For example, the triangle index k for the triangle **210** _{k }has three references to the vertices A, B, and C. The references or the pointers, or the addresses of the coordinate data are stored in the triangle index array T **240** along with the corresponding triangle index. If this triangle index array T **240** is stored in the cache memory, additional cache storage has to be allocated for the triangle index array which further limits the cache allocation for the vertex array V **230**.

The vertex array V **230** may store the vertex information in a unnormalized or a normalized manner. A unnormalized vertex array results in extensive dirty writebacks and increases the processing time while a normalized vertex array reduces or even eliminates dirty writebacks and reduces the processing time.

FIG. 3 is a diagram illustrating arrays for processing unnormalized meshes according to one embodiment of the invention. The mesh pool **220** includes an unnormalized vertex array V **230** and a triangle index array T **240**. For clarity, the arrays are shown storing entries rather than actual memory byte locations.

The unnormalized vertex array **230** contains J entries for J vertices numbered from **0** through J−**1**. Each vertex entry includes three (x, y, z) coordinate values. As shown in FIG. 3, entry **230** _{0 }stores the (X_{0}, Y_{0}, Z_{0}) coordinates of the vertex **0**, entry **230** _{I+1 }stores the (X_{I+1}, Y_{I+1}, Z_{I+1}) coordinates of the vertex I+1, etc.

The triangle index array **240** contains N entries for N triangles numbered from **0** through N−**1**. Each index entry includes three vertex references, vertex **1**, vertex **2**, and vertex **3**. For example, entry **240** _{0 }stores the references **0**, **1** and **3** (i.e., the triangle **0** is formed by three vertices **0**, **1**, and **3**), entry **240** _{L }stores the references **2**, I+**1**, and J−**3** (i.e., the triangle L is formed by three vertices **2**, I+**1**, and J−**3**), etc.

As illustrated in FIG. 3, a triangle index further down the index array T **240** (e.g., index L) may reference a vertex back at the beginning of the vertex array V **230** (e.g., vertex **2**). As the triangle index array T **240** is processed sequentially from entry **0** to entry N−**1**, the vertex array V **230** is referenced in a random manner where an index may reference to a vertex that is located outside the cache locality. For this reason, processing unnormalized meshes results in many dirty writebacks which increases processing time.

FIG. 4 is a diagram illustrating arrays for processing normalized meshes according to one embodiment of the invention. The mesh pool includes a normalized vertex array V **230** and a triangle index array **240**.

The vertex array V **230** is normalized to localize the vertex data in small regions which can be referenced locally by the triangle indices, preserving cache locality and reducing or even eliminating dirty writebacks. To localize the references, redundant vertex data are replicated and stored in the neighborhood of the corresponding vertex locations. For example, the triangle index L references the vertices **2**, I+**1**, and J−**3** (FIG. **3**). As shown in FIG. 3, the references **2** and J−**3** are located outside the cache locality surrounding the vertex I+**1**. The normalized vertex array V **230** duplicates the entries **2** and J−**3** to bring them to the neighborhood of the entry K. Entry **430** _{2 }containing the (X_{2}, Y_{2}, Z_{2}) coordinates is duplicated to occupy entry location K−**1**, entry **430** _{M−3 }containing the (X_{J−3}, Y_{J−3}, Z_{J−3}) coordinates is duplicated to occupy entry location K+**2**. Both the entry locations K−**1** and K+**2** are now in the neighborhood of the entry K which contains the vertex data for the vertex **3** of the triangle index L. Note that the triangle index entry L is now updated to contain the new references K−**1**, K, and K+**2** which correspond to the same vertices **2**, I+**1**, and J−**3** in FIG. **3**.

By bringing the vertex data corresponding to a triangle index into a region that can be referenced locally, the number of cache replacements and dirty writebacks is reduced. Normalized meshes are, therefore, preferred to unnormalized meshes for speeding up the processing time. To further improve the processing time, the normalized meshes are organized according to a window structure.

FIG. 5 is a diagram illustrating arrays for processing normalized meshes using windows according to one embodiment of the invention. The mesh pool **220** includes a normalized vertex array V **230** with windows and a triangle index array T **240**.

The normalized vertex array V **230** is divided into P windows having the same size S. The P windows may be overlapped or distinct. Each of the P windows stores vertex entries that can be referenced entirely by a subset of triangle indices. A window is characterized by its center reference pointer H_{i }and its size S.

Any triangle index T_{i }in a subset RT_{k }of the triangle index array can reference a window L having a center reference H_{i }and a size S_{i}. The window is typically of small size. In other words, there exists a small positive constant S such that S_{i }is less than and equal to S and for all T_{i }within the subset RT:

*H* _{i} *−S/*2*≦R*(*T* _{i})≦*H* _{i} *+S/*2

Where R(T_{i}) is the reference made by the triangle index T_{i}.

As illustrated in FIG. 5, the triangle index T_{k } **240** _{k }references to the window **530** _{L }having a window center at H_{i }with a size S.

As the processor or graphic controller (GC) progresses through the triangle index array T **240**, the normalized vertex array V **230** is referenced on a window-by-window basis. The window essentially “slides” over the entire normalized vertex array **230** as the vertex references are being made. The consequences of this processing method includes the following advantages:

1) An on-line driver can be implemented even for a GC which does not support indexed primitives in hardware. The locality of reference and the sequential nature of the processing enable the writing of triangles or commands to the GC in the background of the geometry or transformation computations. Therefore, the performance advantages of concurrent or parallel processing can be realized.

2) Dirty writebacks from the cache memory can be reduced or eliminated because the window size is typically small, allowing several windows to be located entirely in the cache.

FIG. 6 is a diagram illustrating a performance curve according to one embodiment of the invention. The performance curve includes a horizontal axis corresponding to the triangle number and the vertical axis corresponding to the vertex number. The numbers shown on the axes are merely for illustrative purposes and do not carry any significance. The performance curve shows the processing of the vertices as the triangle number increases. The performance curves includes an upper line **610**, a mesh line **615**, and a lower line **620**.

The upper and lower lines **610** and **620** define the limits of the window. As illustrated in FIG. 6, the window size S is constant throughout the processing of the triangle. The mesh line **615** shows the vertex numbers processed as the number of triangles processed increases. The mesh line **615** fluctuates indicating that the order of vertex references is not in the same sequential order as the triangle indices. However, for any particular triangle index, the vertex references are within the window as defined by the upper and lower lines **610** and **620**.

The performance curve also shows the MIN and MAX values which refer to the pointer of triangle Ti={P_{i1}, P_{i2}, P_{i3}}

FIG. 7 is a flow diagram illustrating a process P**700** to process normalized meshes according to one embodiment of the invention.

Upon START, the process P**700** determines if the meshes have been normalized, i.e., if the vertex array has been normalized (Block B**710**). If not, the process P**700** performs mesh normalization (Block B**715**) and then returns back to block B**710**. If the meshes have been normalized, the process P**700** proceeds to set a normalized mesh flag to inform the GC that the vertex array is normalized (Block B**720**). The process P**700** next obtains the normalized mesh parameters (B**730**). These normalized mesh parameters include the window size S and the mesh ratio R. The mesh ratio R is defined as the ratio of two integers m and n that approximates M and N where M is the number of vertices and N is the number of triangles. The window pointer is a linear growing function of the index i: Hi=R*i where R is a mesh ratio m/n. The mesh ratio m/n provides the closest approximation of M/N.

Next, the process P**700** initializes the pointers for the vertex and triangle index arrays (Block B**740**) and begins mesh processing. The process B**700** slides the window by updating the window pointer Hi=Hi+m (Block B**750**). Then the process B**700** obtains the vertex pointer and vertex coordinates (Block B**760**). Since the vertex array is normalized, the retrieval of the vertex coordinates takes place in the memory locality. The process P**700** then performs graphic transformation and/or rendering on the vertex information and concurrently send the transformed data to the graphics processor on an on-line basis (Block B**770**). The process P**700** next updates the triangle index I=I+n (Block B**780**).

The process P**700** then determines if all the triangles have been processed (Block B**785**). If not, the process P**700** updates the triangle index I (Block B**790**) and returns to obtain the next vertex pointer for the updated triangle index I (Block B**750**). If all the triangles have been processed, the process P**700** terminates.

Although the process P**700** is shown in sequential manner, many of the operations can be performed in parallel. For example, the graphic transformation/rendering in Block B**770** and/or the transfer of graphic data to the graphic processor in Block B**780** can be performed concurrently with the retrieval of vertex coordinates in Block B**760**.

The processing of unnormalized or normalized meshes can also be realized by hardware using a mesh processor to achieve even faster processing time.

FIG. 8 is a diagram illustrating a mesh processor **132** according to one embodiment of the invention. The mesh processor **132** includes a parameter register **810**, a triangle index array **820**, an address comparator and generator **830**, a vertex buffer **840**, a data fetcher **850**, a multiplexer **860**, and a graphics engine **870**. The mesh processor **132** is coupled to a graphic bus **122** and to the graphics processor **125** as shown in FIG. **1**.

The parameter register **810** stores the operational parameters for the graphics engine **870**. These parameters include at least the normalized mesh flag, the window size, and the mesh ratio. The normalized mesh flag informs the graphics engine if the vertex buffer **840** is normalized.

The triangle index array **820** stores the triangle indices and the corresponding vertex references. The triangle index arrays **820** is loaded by the processor **110** or the graphics processor **125** via the graphic bus **122**. The triangle index array **820** provides the triangle indices and the vertex references to the graphics engine **870** and the address generator and comparator **830**. Normally, the triangle index array **820** is accessed sequentially as the graphics engine **870** processes the mesh pool. Therefore, the addressing mechanism for the triangle index array **820** is simple and can be implemented by a counter. Alternatively, the graphics engine **870** may address the triangle index array **820**.

The address comparator and generator **830** generates the addresses to the vertex buffer **840** (and to the triangle index array **820** if necessary), and performs address comparison. The address comparator and generator **830** determines the addresses for the vertex buffer **840** using the reference data provided by the triangle index array **820**. The address comparator and generator **830** also compares the generated addresses with the window size to determine if a window boundary has been crossed. Depending on the result of the address generation and comparison, the address comparator and generator **830** sends a control signal to the data fetcher **850** and a selection signal to the multiplexer **860**. For example, if it is determined that the vertex buffer **840** does not contain the vertex information, then the address comparator and generator **830** sends a control signal to the data fetcher **850** to fetch the necessary information and to switch the multiplexer to select the data from the data fetcher **850** directly. This situation is particularly relevant when the meshes are unnormalized which have many references that are outside the vertex buffer locality.

The vertex buffer **840** stores the vertex information including the vertex coordinate values. The vertex buffer **840** is typically allocated with a size compatible with the window size of the normalized meshes or with a predetermined size for unnormalized meshes. In one embodiment, the size of the vertex buffer **840** is a multiple of the window size so that a number of windows of the vertex data can be stored in the vertex buffer **840** at the same time. In addition, the vertex buffer **840** may be implemented as a circular buffer so that as a window is no longer needed, a new window may be loaded in to maintain continuous data fetching. The loading of the vertex buffer **840** may be carried out in a pipeline fashion such that while a set of data are read by the graphics engine **870**, another set of new data is written in.

The data fetcher **850** fetches the vertex information from the external memory via the graphics bus **122**. The data fetcher **850** receives control signals from the address comparator and generator **830** to perform the fetching. If the vertex buffer **840** is implemented as a circular buffer, the address comparator and generator **830** sends a control signal to the data fetcher **850** when a window boundary has been crossed so that the data fetcher **850** can begin fetching new data to the vertex buffer **840**. In addition, when the data is not in the vertex buffer **840**, the data fetcher **850** can fetch the needed data and bypasses the vertex buffer **840** to send to the multiplexer **860** directly. This situation may occur when the meshes are not normalized or when the references occasionally cross a reference locality.

The multiplexer **860** provides a selection of the data path for the vertex information to the graphics engine **870**. The multiplexer **860** receives the select signal from the address comparator and generator **830**.

The graphics engine **870** receives the operational parameters from the parameter register **810**, generates control signals to the triangle index array **820** and the address comparator and generator **830**, and receives the vertex information through the multiplexer **860**. The graphics engine **870** provides the processed data to the graphics processor for further processing or display. The graphics engine **870** may perform a preliminary processing or a graphic transformation before sending data to the graphics processor.

FIG. 9 is a flow diagram illustrating a process P**900** to normalize meshes with the same window size according to one embodiment of the invention.

Upon START, the process P**900** determines the average window size S for the vertex array that works for approximately N% of the vertices (Block B**910**). In other words, about N% of the vertices can be referenced locally within a window of size S. The value N is determined according to some predefined criteria. Typically, N% is about 90%. The process P**900** then initializes the triangle index I for triangle T_{i }(Block B**920**). Next, the process P**900** obtains the triangle index T_{i }(Block B**930**). From the triangle index T_{i}, the process P**900** obtains the vertex references and determines the addresses of the vertices referenced by T_{i }(Block **940**).

The process P**900** then determines if T_{i }references a vertex that lies outside the window (Block B**945**). This can be performed by comparing the addresses of the vertex with the upper and lower limits formed by the window center addresses and the window size S. If the referenced vertex does not lie outside the current window, the process P**900** determines if all the triangle indices have been processed (Block B**985**). If the end of the triangle index array has been reached, the process P**900** terminates. If the end of the triangle index array has not been reached, the process P**900** updates the triangle index I (Block B**990**) and returns to Block B**930**.

If the referenced vertex lies outside the current window, the process P**900** increments the window size and the vertex array size by one in anticipation of a copy of the vertex information to the current window (Block B**950**). The process P**900** then copies the vertex information from the referenced location to the current window (Block B**960**). The process P**900** then updates the vertex array with the new window size (B**970**). For example, the vertex array may be pushed down one location to make room for the newly acquired entry. Then the process P**900** updates the triangle index array to reflect the new references which include the T_{i }references. The process P**900** then goes to block B**985** to determine if the end of the triangle index array has been reached.

FIG. 10 is a flow diagram illustrating a process P**1000** to normalize meshes with different window sizes according to one embodiment of the invention.

Upon START, the process P**1000** determines the window sizes S_{1}, . . . S_{k }and the mesh ratios R_{1}, . . . , R_{k }for the M regions of the vertex array (Block **1010**). For each region i, the process P**1000** uses the corresponding window size S_{i }and proceeds using the process P**900** as described in FIG. 9 (Block B**1020**). Then the process P**1000** determines if M regions have been processed (Block B**1030**). If not, the process P**1000** goes to the next region (Block B**1040**) and returns back to Block B**1020** to process the next region. If all regions have been processed, the process P**1000** terminates.

FIG. 11 is a diagram illustrating an example of an object **1100** according to one embodiment of the invention. The object **1100** includes **9** triangles numbered **0** through **8**. The triangle indices are shown in the comer of each triangle. The vertices of **9** triangles are A, B, C, D, E, F, G, H, I and J. Many vertices are common to several triangles.

FIG. 12 is a diagram illustrating arrays for processing unnormalized meshes in the example of FIG. 11 according to one embodiment of the invention. The mesh pool **1200** includes an unnormalized vertex array **1220** and a triangle index array **1210**. The unnormalized vertex array **1220** has **10** entries numbered **0** through **9** corresponding to **10** vertices A, B, C, D, E, F, G, H, I, and J. Each entry contains three coordinates values. For example entry **0** contains (X_{A}, Y_{A}, Z_{A}) for vertex A, entry **1** contains (X_{B}, Y_{B}, Z_{B}) for vertex B, etc.

The triangle index array **1210** has 9 entries numbered **0** through **8** corresponding to 9 triangles. Each entry contains the vertex references which define the triangle. For example, entry **0** contains the vertex references A, B, C, entry **1** contains the vertex references A, D, E, etc.

FIG. 13A is a diagram illustrating spikes in a performance curve caused by processing unnormalized meshes in the example of FIG. 11 according to one embodiment of the invention. The horizontal axis shows the triangle number and the vertical axis shows the vertex number. Since the vertex array is unnormalized, there is no duplication of vertex numbers on the vertical axis. The dots shown in the diagram shows the vertices for the corresponding triangle. For example, the three dots A, B, and C at the vertical line **0** correspond to the three vertices A, B, and C for triangle **0**.

Suppose the cache locality is defined as **4**, i.e., the cache boundary is between vertices E and F, then if the vertices of a triangle are referenced across the cache boundary, a spike results, indicating that a dirty writeback may be necessary to bring the outside reference to the cache. In the diagram, there are three spikes for triangles **3**, **4**, and **5**.

FIG. 13B is a diagram illustrating the reference pointers stored in the triangle index array for the unnormalized meshes in the example of FIG. 11 according to one embodiment of the invention. For example, triangle **5** references vertices **4**, **7** and **9**.

FIG. 14 is a diagram illustrating arrays for processing normalized meshes in the example of FIG. 11 according to one embodiment of the invention. The mesh pool now includes a normalized array **1420** and the triangle index array **1210**.

The normalization of the vertex array copies the vertex entries in localized window. In this example, the window size becomes **7**. Since a fixed window size is used, there may be empty entries in a window. For example, entry **6** in the vertex array **1420** is empty. In this example, triangles **0**, **1**, **2**, and **3** reference all vertices stored in window p**1**; triangles **4**, **5**, **6**, **7**, and **8** reference all vertices stored in window P**2**. Since there is no crossing of window boundary, the window reference locality is preserved.

FIG. 15A is a diagram illustrating a performance curve for processing normalized meshes with separated vertex windows in the example of FIG. 11 according to one embodiment of the invention. The diagram includes two groups **1510** and **1520**. The vertical axes now have redundant vertex numbers. For example, vertices D, E, and F are duplicated. It is seen that there is no spike because there is no reference that crosses a window boundary. The groups **1510** and **1520** contain the vertex references in the first and second windows, respectively. The two groups are separated.

FIG. 15B is a diagram illustrating the reference pointers stored in the triangle index array for the normalized meshes in the example of FIG. 11 according to one embodiment of the invention. It is seen that the references have been updated to reflect the new references caused by the duplication of the vertex entries in the vertex array.

Therefore, the present invention provides a technique to process normalized meshes and to normalize unnormalized meshes. The technique helps improve the access time of the vertex array by grouping the vertex data in localized windows. The technique can be realized by software or hardware and can be used in conjunction with a graphics processor to improve the performance.

While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, which are apparent to persons skilled in the art to which the invention pertains are deemed to lie within the spirit and scope of the invention.

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Classifications

U.S. Classification | 345/419, 345/537 |

International Classification | G06T15/00, G06T17/20 |

Cooperative Classification | G06T17/20 |

European Classification | G06T17/20 |

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